Ketone Bodies, Eicosanoids & Atherosclerosis

Ketone bodies are small fuel molecules the liver makes from fat when glucose runs low; eicosanoids are short-range lipid messengers that orchestrate inflammation, clotting, and pain; and atherosclerosis is the slow arterial disease in which cholesterol-rich plaques inflame, rupture, and trigger clots. Three different lipid stories on one shared stage: human disease.

This matters because these three decide emergencies. Diabetic ketoacidosis can kill in hours, aspirin prevents heart attacks by blocking eicosanoid synthesis, and plaque rupture causes most heart attacks and strokes.

Key Concepts

• Ketone bodies: acetoacetate, beta-hydroxybutyrate, and acetone — made in liver mitochondria from acetyl-CoA when fat breakdown outpaces the Krebs cycle. The liver cannot use them but the brain, heart, and muscle can.
• Ketogenesis vs ketoacidosis: mild ketone production during fasting is normal; runaway production in uncontrolled diabetes causes dangerous blood acidity.
• Eicosanoids: 20-carbon signals from arachidonic acid — prostaglandins (pain, fever, inflammation), thromboxanes (platelet clumping), leukotrienes (allergy, asthma).
• COX-1 and COX-2: the enzymes starting prostaglandin synthesis; aspirin blocks COX-1 irreversibly, which is why one low dose protects platelets for their whole lifespan.
• Atherosclerosis stages: endothelial injury → LDL oxidation → macrophage foam cells → fatty streak → fibrous plaque → rupture → thrombosis. Most heart attacks come from thin-capped plaques that were not severely narrowing.

How It Works

Trace a fasting day. As liver glycogen empties, glucagon rises and fat floods out of adipose tissue. Beta-oxidation makes acetyl-CoA faster than the Krebs cycle can accept it, so the liver condenses the surplus into ketone bodies for the brain — which cannot burn fatty acids directly. Meanwhile injured tissue releases arachidonic acid from membranes, and COX enzymes convert it within seconds into prostaglandins that summon inflammation and thromboxanes that make platelets sticky. In artery walls, oxidised LDL is swallowed by macrophages that gorge into foam cells, and over decades inflammation builds this into a plaque. When its fibrous cap tears, collagen meets blood, platelets clot in minutes, and the artery occludes.

Worked Example

How far above normal are ketones in diabetic ketoacidosis? Normal is below 0.6 mmol/L; DKA commonly exceeds 3–4 mmol/L. Take 4.0 mmol/L with about 5 litres of blood. Step 1: total ketones — 4.0 × 5 = 20 mmol. Step 2: normal total — 0.6 × 5 = 3 mmol. Step 3: 20 ÷ 3 ≈ 6.7. So DKA carries roughly seven times the normal ketone load — enough to overwhelm blood buffers, drop pH, and trigger the deep rapid Kussmaul breathing that blows off acid as CO₂.

Common Misconceptions

• Ketones are always dangerous. Nutritional ketosis from fasting is controlled and mild; ketoacidosis is uncontrolled and severe, needing insulin deficiency plus dehydration.
• Aspirin thins the blood. It does not dilute anything — it permanently disables platelet COX-1, so platelets cannot make thromboxane that makes them clump.
• Atherosclerosis is just cholesterol clogging pipes. It is an inflammatory disease of the artery wall; cholesterol is necessary, but inflammation, oxidation, and rupture are what kill.

Real-World Applications

• DKA is treated with insulin, fluids, and potassium — insulin switches ketogenesis off at its source.
• Low-dose aspirin after a heart attack or stent keeps platelets quiet via COX-1 blockade.
• Statins stabilise plaques partly through anti-inflammatory effects, not just cholesterol lowering.
• Ketone meters let people on therapeutic ketogenic diets (for epilepsy) verify they are in safe nutritional ketosis.

Ketone bodies rescue the brain when glucose fails, eicosanoids turn membrane fat into instant inflammatory and clotting signals, and atherosclerosis turns oxidised LDL plus inflammation into rupturing plaques. DKA shows ketones at seven times normal, aspirin disarms platelets through COX-1, and plaque rupture — not gradual narrowing — causes most heart attacks.